It has long been necessary and desirable to heat various types of liquids in tanks, as for example liquids used in plating of various kinds as well as in preparing articles for plating and similar processes, the liquids being both acid and alkaline as well as corrosive in many instances.
Inasmuch as such liquids may destroy certain heating elements, such elements must be of composition to resist that action. In acid conditions quartz tube immersion heaters generating infra-red radiation are particularly suitable and well known.
In alkaline conditions, metal tubular heaters for generating radiation are frequently used, though they would be damaged in acid conditions.
In all such instances and environments, the liquid level is necessary to be maintained, as lowering of the level below the upper end of the hot zone of radiating heaters, may result in damage and/or destruction of such heaters, and thus level indicating warning and control systems are particularly desirable.
Such controls have in the past taken the form of float means involving linkages and micro-switches, which are unreliable and adversely affected by the environment.
Other controls known as proximity types have also been used, but these involve delicate parts and circuitry including capacitors which may be initially workable but do not stand up under the conditions to which they are subjected, and are thus affected as to accuracy and reliability.
Thus the instant invention, which embodies an entirely new approach, is particularly suitable since the parts may be of rugged construction and in any event are not subject to many of the problems of prior liquid level responsive control means, being simple in construction and operation with fail safe means to provide maximum effectiveness and instant response.